This invention is related to dynamoelectric machines such as an electrical alternator, including those of a type particularly adapted for use in motor vehicle applications. These devices are typically mechanically driven using a drive belt wrapped on a pulley connected to the crankshaft of the vehicle's internal combustion engine. The belt drives a pulley on the alternator which rotates an internal rotor assembly to generate alternating current (AC) electrical power. This alternating current electrical power is rectified to direct current (DC) and supplied to the motor vehicle's electrical bus and storage battery.
While alternators have been in use in motor vehicles for many decades, today's demands on motor vehicle design, cost, and performance have placed increasing emphasis on the design of more efficient alternators. Today's motor vehicles feature a dramatic increase in the number of electrical on-board systems and accessories. Such electrical devices include interior and exterior lighting, climate control systems; and increasingly sophisticated power train control systems, vehicle stability systems, traction control systems, and anti-lock brake systems. Vehicle audio and telematics systems place further demands on the vehicle's electrical system. Still further challenges in terms of the output capacity of the motor vehicle's electrical alternators will come with the widespread adoption of electrically assisted power steering and electric vehicle braking systems. Compounding these design challenges is the fact that the demands on the vehicle's electrical system vary widely, irrespective of the engine operating speed which drives the alternator and changes through various driving conditions.
In addition to the challenges of providing high electrical output for the vehicle electrical alternator, further constraints include the desire to minimize the size of the alternator with respect to under hood packaging limitations, and its mass which relates to the vehicle's fuel mileage.
In addition to the need of providing higher electrical output, designers of these devices further strive to provide high efficiency in the conversion of mechanical power delivered by the engine driven belt to electrical power output. Such efficiency translates directly into higher overall thermal efficiency of the motor vehicle and thus into fuel economy gains. And finally, as is the case with all components for mass-produced motor vehicles, cost remains a factor in the competitive offerings of such components to original equipment manufacturers.
Enhanced efficiency of the alternator can be provided through various design approaches. The alternator uses a rotating rotor assembly, which creates a rotating alternating polarity magnetic field. This rotating magnetic field is exposed to an annular stator assembly which closely surrounds the rotor assembly. Electrical conductor windings are embedded within the stator assembly. As is well known in the art, it is desirable to cool the conductors because the electrical resistance of the conductor is proportional to the temperature of the wire. Since the resistance of the conductor is inversely proportional to alternator output and efficiency, cooling of the stator winding is an important factor for improving alternator output and efficiency.
Unfortunately, many stator core assemblies utilize windings that do not promote cooling of the conductors. Some alternator designs employ conventional wire conductors having a round cross sectional shape wound into radially projecting slots formed In the stator core. These round cross-sectional wires are nested against other turns of wire in the slots in a random winding pattern that results in the turns being bunched together with no or very little openings to allow cooling air to pass in between the conductors. This arrangement thus limits convective cooling of the stator winding. Accordingly, there exists a need for a stator assembly that increases the efficiency of the alternator by improving the cooling of the stator winding, while at the same time preventing unwanted increases in size and cost of the alternator or dynamoelectric machine.